It is an increasingly common problem for tendons and other soft connective tissues to tear or to detach from associated bone. One such type of tear or detachment is a “rotator cuff” tear, wherein the supraspinatus tendon separates from the humerus, causing pain and loss of ability to elevate and rotate the arm. Complete separation of tissue from the bone can occur if the shoulder is subjected to gross trauma, but typically, the tear begins as a small lesion, especially in older patients.
To repair a torn rotator cuff, the typical course is to do so surgically, through a large incision. There are two types of open surgical approaches for repair of the rotator cuff, one known as the “classic open” and the other as the “mini-open”. The classic open approach requires a large incision and complete detachment of the deltoid muscle from the acromion to facilitate exposure. The cuff is debrided to ensure suture attachment to viable tissue and to create a reasonable edge approximation. In addition, the humeral head is abraded or notched at the proposed soft tissue to bone reattachment point, as healing is enhanced on a raw bone surface. A series of small diameter holes, referred to as “transosseous tunnels”, are “punched” through the bone laterally from the abraded or notched surface to a point on the outside surface of the greater tuberosity, commonly a distance of 2 to 3 cm. Finally, the cuff is sutured and secured to the bone by pulling the suture ends through the transosseous tunnels and tying them together using the bone between two successive tunnels as a bridge, after which the deltoid muscle must be surgically reattached to the acromion.
The mini-open technique differs from the classic approach by gaining access through a smaller incision and splitting rather than detaching the deltoid. Additionally, this procedure is typically performed in conjunction with arthroscopic acromial decompression. Once the deltoid is split, it is refracted to expose the rotator cuff tear. As before, the cuff is debrided, the humeral head is abraded, and the so-called “transosseous tunnels” are “punched” through the bone or suture anchors are inserted. Following the suturing of the rotator cuff to the humeral head, the split deltoid is surgically repaired.
Less invasive arthroscopic techniques continue to be developed in an effort to address the shortcomings of open surgical repair. Working through small trocar portals that minimize disruption of the deltoid muscle, surgeons have been able to reattach the rotator cuff using various suture anchor and suture configurations. The rotator cuff is sutured intracorporeally and an anchor is driven into bone at a location appropriate for repair. Rather than thread the suture through transosseous tunnels which are difficult or impossible to create arthroscopically using current techniques, the repair is completed by tying the cuff down against bone using the anchor and suture.
The skill level required to facilitate an entirely arthroscopic repair of the rotator cuff is fairly high. Intracorporeal suturing is clumsy and time consuming, and only the simplest stitch patterns can be utilized. Extracorporeal knot tying is somewhat less difficult, but the tightness of the knots is difficult to judge, and the tension cannot later be adjusted. Also, because of the use of suture anchors to provide a suture fixation point in the bone, the knots that secure the soft tissues to the anchor by necessity leave the knot bundle on top of the soft tissues. In the case of rotator cuff repair, this means that the knot bundle is left in the shoulder capsule where it can be felt by the patient postoperatively when the patient exercises the shoulder joint. So, knots tied arthroscopically are difficult to achieve, impossible to adjust, and are located in less than optimal areas of the shoulder. Suture tension is also impossible to measure and adjust once the knot has been fixed.
There are various suture anchor designs available for use by an orthopedic surgeon for attachment of soft tissues to bone. A number these designs include use of a locking plug which is forced into a cavity of the anchor body to secure the suture therein. Although there is some merit to this approach for eliminating the need for knots in the attachment of sutures to bone, a problem with being able to properly set the tension in the sutures exists. The user is required to pull on the sutures until appropriate tension is achieved, and then to set the plug portion into the suture anchor portion. This action increases the tension in the sutures, and may garrote the soft tissues or increase the tension in the sutures beyond the tensile strength of the material, breaking the sutures. In addition, the minimal surface area provided by this anchor design for pinching or locking the sutures in place will abrade or damage the suture such that the suture's ability to resist load will be greatly compromised. Additionally, once the suture is fixed, the suture cannot be adjusted or retensioned. This is a shortcoming of such designs because it is not uncommon for a physician to desire to reposition or adjust the tissue location and suture after the anchor has been set.
An example of a suture anchor that addresses some of the above mentioned shortcomings is shown in FIGS. 1A and 1B. Anchor 1 may include a rotatable or pivoting cam 5 to lock suture 28 within suture anchor 1. In this embodiment, suture leg 28a may be bound or connected to tissue (tissue not shown), and suture leg 28b may be free to be adjusted by the practitioner. In FIG. 1A, the bound suture tension (T1) is minimal as the tissue may not be adjacent the anchor 1, and the practitioner is applying open suture tension (T2) to draw the suture 28 around the cam 5 and essentially draw the tissue attached to bound suture leg 28a closer to the suture anchor 1 and into engagement with the bone. As the bound suture tension (T1) increases, due to the tissue being closer to its target location, T1 may begin to approximate or exceed the open suture tension (T2), and the resulting frictional force F(T1+T2) between the cam 5 and the suture 28 may cause the cam 5 to rotate clockwise, and clamp down and lock or wedge the suture 28 as shown in FIG. 1B. Problematically, as the coefficient of friction between the cam 5 and suture 28 decreases, the suture 28 may slip and cam 5 may not rotate or the lock force may not be sufficient, i.e. the lock mechanism may have a tendency to fail.
Thus, a suture anchor and method for repairing rotator cuff or fixing other soft tissues to a target bone tissue, wherein a lock mechanism provides more control to the user, allows the suture to be re-tensioned, maintains a strong locking force and functions reliably in a low friction environment is still desirable.